1. Field of the Invention
The present invention relates to a method and an apparatus for molding and curing a tyre for vehicle wheels.
2. Description of the Related Art
In a tyre production cycle it is provided that following a building process in which the different tyre components are made and/or assembled, a molding and curing process is carried out which aims at defining the tyre structure in accordance with a desired geometry, usually exhibiting a particular tread pattern.
For the purpose, the tyre is closed in a molding cavity defined internally of a vulcanisation mold and shaped in accordance with the geometric configuration of the outer surfaces of the tyre to be obtained.
A tyre generally comprises a toroidally ring-shaped carcass including one or more carcass plies, strengthened with reinforcing cords lying in radial planes, i.e. containing the rotation axis of the tyre. Each carcass ply has its ends integrally associated with at least one annular reinforcing metal structure, usually known as bead core, constituting the reinforcing piece at the beads, i.e. at the radially internal ends of said tyre, the function of which is to enable assembling of the tyre with a corresponding mounting rim. Placed crownwise to said carcass is a band of elastomer material, called tread band, in which at the end of the curing and vulcanisation steps a raised pattern is formed for ground contact. A reinforcing structure usually known as belt structure is placed between the carcass and tread band. This structure in the case of tyres for cars usually comprises at least two radially superposed strips of rubberised fabric provided with reinforcing cords, usually of metal material, disposed parallel to each other in each strip and in crossed relationship with the cords of the adjacent strip, preferably symmetrically disposed with respect to the equatorial plane of the tyre.
Preferably, said belt structure further comprises, at a radially external position thereof, at least on the ends of the underlying strips, a third layer of textile or metallic cords as well, that are disposed circumferentially (at 0 degrees).
Finally, in tyres of the tubeless type i.e. devoid of an air tube, a radially internal layer generally called liner is present which has imperviousness features to ensure the tyre air-tightness.
To the aims of the present invention it is to be pointed out that by the term “elastomer material” it is intended a composition comprising at least one elastomer polymer and at least one reinforcing filler. Preferably, this composition further comprises additives, such as cross-linking and/or plasticizing agents, for example. By virtue of the presence of the cross-linking agents, this material can be cross-linked through heating, so as to form the final manufactured article.
There are molding and curing methods in which a green tyre put on a rigid toroidal support is arranged within the mold. Said methods are preferably employed for tyres that, following recent building processes, are produced starting from a limited number of elementary semifinished products fed onto a toroidal support the outer profile of which is coincident with that of the radially internal surface of the tyre that is wished to be produced. Said toroidal support is moved, preferably by a robotized system, between a plurality of stations in each of which, through automated sequences, a particular building step of the tyre is carried out (see document EP 0 928 680 in the name of the same Applicant, for example).
The European Patent Application published under No. 0 976 533 in the name of the same Applicant discloses a method and an apparatus for molding and curing tyres for vehicle wheels in which the green tyre built on a toroidal support is closed in a vulcanisation mold; subsequently steam or other fluid under pressure is fed into at least one gap for fluid diffusion created between the outer surface of the toroidal support and inner surface of the tyre.